The landing party discovers a survivor in the ruins, LieutenantHarold. Spock quickly locates the presence of other life forms nearby, but, not any colony survivors. His tricorder reads them as cold-blooded creatures, but definitely not Human. O'Herlihy scouts them out, but is immediately disintegrated by an alien weapon as the landing party is bombarded by a massive shelling attack.

"Captain, I see something...!"

At the same time, the Enterprise comes under attack in orbit by an unidentified starship. With her deflector screens up, the Enterprise cannot beam up the landing party. Kirk orders Sulu to return fire with the phaser banks, but, it has little effect as the alien ship has screens up, as well. Kirk orders the use of photon torpedoes, but, the torpedoes are ineffective, as the alien is too far away even for visual contact. The Captain orders Sulu to take whatever action is necessary to protect the Enterprise, be it leaving orbit or engaging maximum warp. Sulu opts for the former and take the ship away from Cestus III.

Kirk makes his way to the colony's arsenal and retrieves a grenade launcher. Spock and Kelowitz rendezvous with him as the first officer reports that the enemy troops are moving their location. Kelowitz gives Kirk his best guess as to where they have moved to and Kirk launches the grenade in that direction. The tactic proves successful as the aliens begin to decamp back to their ship, allowing Sulu to return with the Enterprise and retrieve the landing party and quickly set a pursuit course of the attacking ship.

In sickbay, Harold tells Kirk and Spock of the attack on the colony. The aliens had knocked out their phasers with their first salvo, leaving the colony defenseless and confirms Kirk's earlier theory that the aliens had faked the message from the colony diverting the Enterprise to Cestus III in an attempt to destroy the Enterprise, the only protection in that part of the Federation. Such a move, a prelude to invasion, suggests the correct course: overtake and destroy the enemy, before he can return to his home base and report. The Captain orders the ship to battlestations and to warp 6 to overtake the aliens.

The aliens, aware that the Enterprise is after them, jumps to warp 6, as well. Kirk orders warp 7 engaged, drawing concern from Spock and Scotty that a sustained warp 7 speed will be hazardous to the Enterprise's engines. Spock argues against destroying the enemy vessel, on the basis of respect for sentient life. Kirk disagrees; his opinion is that a crime has been committed and the perpetrators must be punished. Sulu reports that the aliens have moved to warp 7, as well. Kirk, mulling over his options, orders the ship to warp 8 and all weapons departments at battle ready.

Closing at warp 8, the Enterprise records a scanning beam from an uncharted solar system at 2466 PM. The alien is not approaching this system; it appears that a third party is "curious" about the Enterprise. The alien abruptly begins to slow, going quickly to sublight speed until finally stopping dead in space. Kirk closes for the kill, but the Enterprise is soon slowed to sublight, as well, stopped dead like the alien with all power to the engines and weapons simply cut off.

The architects of this reveal themselves: the Metrons, an advanced race who regard intrusion into their space for the purpose of conflict as entirely unacceptable. They remove Kirk from the Enterprise and the Gorncaptain from the alien vessel and deposit both of them on a suitably-prepared world. There, they will settle their differences, using strength and ingenuity.

The Gorn captain is reptilian, large, and very strong – but quite slow. Kirk is able to evade him initially, but knows he can't evade him indefinitely. He'll have to find a way to defeat an opponent who is far stronger and tougher.

The key may lie in a comment the Metron made, that the prepared environment contains elements suitable for fabricating weapons. Attack and evasion continue for some time, with Kirk narrowly evading death at the Gorn's claws. Back on the Enterprise, the crew is unable to restore power to the engines and the weapons and remains immobilized. The Metrons reestablish communications and inform the crew that Kirk is losing the battle. In view of his impending death, they allow the crew to watch what is happening on the viewscreen.

The Gorn finally communicates: it proposes that Kirk cease trying to evade him, and promises in exchange to be merciful and quick. Kirk compares this offer to the "mercy" shown at Cestus III; this enrages the Gorn, who tells Kirk his people regard Cestus III as part of their space. From the Gorn perspective, they were repelling an invading force. Watching from the bridge, McCoy posits that it is perhaps they who are in the wrong. Spock agrees it is possible.

As the conflict continues, Kirk remembers an old formula: gunpowder. Using sulfur, coal, potassium nitrate, diamonds, and a bamboo-like plant, Kirk constructs a makeshift cannon. Spock, amazed by the Captain's ingenuity, posits that Kirk might be successful, if he can complete construction of the cannon before the Gorn closes in for the kill. Moments from a fatal attack, Kirk rips up his own uniform to make a fuse and uses the metallic recording-translating device provided by the Metrons to spark the coal, allowing Kirk to touch off his crude device which incapacitates the Gorn.

Kirk has won the contest, but stops short of delivering the fatal stroke to the Gorn captain. He yells out loud to the unseen Metrons that he won't kill him and that they will have to find their entertainment elsewhere. The Gorn suddenly disappears and the Metron appears, expressing surprise: their analysis did not prepare them for Kirk's demonstration of mercy towards his helpless opponent. The Metron informs Kirk that he has returned the Gorn to his ship and will destroy him for Kirk, if he so chooses. Kirk declines and claims that the Federation and the Gorn can talk their dispute over and perhaps reach and agreement. This also impresses the Metron and theorizes that although Humanity is still half-savage, perhaps in several thousand years it will be civilized enough to be of further interest to the Metrons. Kirk is returned to the Enterprise, where he discovers that the ship has been relocated five hundred parsecs away from the Metron solar system.

"Captain's log, stardate 3045.6. The Enterprise has responded to a call from Earth observation outpost on Cestus III. On landing, we have discovered that the outpost has been destroyed."

"Captain's log, supplement. We have beamed back to the Enterprise and immediately set out in pursuit of the alien vessel. It appears to be headed towards a largely unexplored section of the galaxy."

"Captain's log, stardate 3046.2. We are in hot pursuit of the alien vessel which destroyed the Earth outpost on Cestus III."

"The Enterprise is dead in space, stopped cold during her pursuit of an alien raider by mysterious forces... and I have been somehow whisked off the bridge and placed on the surface of an asteroid, facing the captain of the alien ship. Weaponless, I face the creature the Metrons called a Gorn: large, reptilian. Like most Humans, I seem to have an instinctive revulsion to reptiles. I must fight to remember that this is an intelligent, highly advanced individual, the captain of a starship like myself. Undoubtedly, a dangerously clever opponent."

"This is Captain James Kirk of the Starship Enterprise. Whoever finds this, please get it to Starfleet Command. I'm engaged in personal combat with a creature apparently called a Gorn. He's immensely strong. Already, he has withstood attacks from me that would have killed a Human being. Fortunately, though strong, he is not agile. The agility and I hope the cleverness, is mine."

"The Metrons, the creatures that sent us both here, said that the surface of the planet provides the raw material... to construct weapons. There's very little here – scrub brush, rocks, an abundance of mineral deposits, but no weapons in the conventional sense. Still, I need to find one; bare-handed against the Gorn, I have no chance."

"A large deposit of diamonds on the surface. Perhaps, the hardest substance known in the universe. Beautifully crystallized and pointed, but too small to be useful as a weapon. An incredible fortune in stones, yet I would trade them all for a hand phaser or a good, solid club. Yet, the Metrons said there would be weapons... if I could find them. Where? What kind?"

"This may be my last entry. I am almost exhausted. Unless I find the weapon the Metron mentioned, I have very little time left. Native sulfur, diamonds... This place is a mineralogist's dream! Yet... there is something about sulfur... something very old. Something... if only I could remember."

This teleplay was credited to an original story by Fredric Brown, also titled "Arena", that was first published in 1944 on the pages of Astounding Science Fiction magazine, though Robert Justman and Herb Solow wrote in Inside Star Trek: The Real Story, that Gene L. Coon wrote his script as an original (over the course of a weekend), unaware of Brown's story, and only sought permission to "adapt" the story after the slight similarities were pointed out to him. Brown was more than happy to hear that Star Trek decided to use one of his stories, and probably never found out the real plot behind it.

In his final speech, the Metron informs Kirk that, because he demonstrated mercy, he will not be destroyed. Initially, they said they planned to destroy the loser, "in the interests of peace". In Coon's script, in dialog not aired, the Metron admits that they had, all along, planned to actually destroy the ship of the winner of the personal combat, because that race would represent the greater danger to them. James Blish preserves this disclosure in his novelization in Star Trek 2.

"Metron" is similar to Metatron, an angel in Judaism. The name means "instrument of change" in Greek. The name of the planet, Cestus III, refers to gladiatorial combat. A cestus is a type of boxing glove, consisting of strips of iron wrapped in leather, which gladiators wore in the arena.

Vic Perrin's dialog as the Metron has a few phrases that are quite similar to his "Control Voice" narration on The Outer Limits.

The word "SCRIPT" is misspelled.

In the closing credits of the show, the title for Script Supervisor is misspelled "SCPIPT SUPERVISOR". This typo continues for several episodes within the closing credits.

The scenes on the planet surface were filmed at Vasquez Rocks, California, the same location used for "Shore Leave", "Friday's Child" and several other Star Trek productions. The area of Kirk's fight with the Gorn, in front of a jagged rock face known to fans as "Gorn Rock", [1] was also seen in the film Bill & Ted's Bogus Journey. The two main characters in that film, after watching "Arena" on television, also visited Vasquez Rocks, California. Furthermore, the diner in Jay and Silent Bob Strike Back is called the "Arena Diner", named after this episode since that particular scene in the film was also filmed in Vasquez Rocks. In the 1998 movie Free Enterprise, two of the characters goof around there in Trek-style costumes. The rocks also appear in an homage to this scene in Paul with Simon Pegg playing Kirk and Nick Frost as the Gorn (and wearing a Gorn mask). They leave quickly when tourists to Vasquez Rocks see them acting out. The entire first three seasons of Mighty Morphin Power Rangers had the command center at the top of the cliff.

In an episode of "The Big Bang Theory" ("The Bakersfield Expedition")[2], the main male characters - Leonard, Sheldon, Raj, and Howard dressed as Picard, Data, Worf, and a Borg - stop at the Vasquez Rocks on their way to Comic Con in Bakersfield to take pictures in character. (Unfortunately, Leonard's car is stolen while they aren't looking.)

The fort set (Cestus III), retouched here with science-fiction trappings and location signs, can be seen in several early episodes of The Wild Wild West, most prominently in the episode "The Night of the Sudden Plague." It also is an important part of the coincidentally-titled Mission: Impossible episode, "Trek." This set was directly adjacent to Vasquez Rocks – so close that in an episode of Bat Masterson, entitled "Dagger Dance" (1961, with Byron Morrow) both the fort and the distinctive peaks of Vasquez Rocks appear in the same shot. In some shots Vasquez Rocks can be seen from the set in "Arena" itself. The fort set plays a major role in the 1964 Bonanza episode "Alias Joe Cartwright." The fort's walls and crenelations are clearly visible throughout the episode. The Vasquez Rocks area is used for the traveling segments back and forth to town. According to Eddie Paskey's website, it was also used for the film Beau Geste. [3] According to Jerry L. Schneider's "Vasquez Rocks" web page on Movie Making Locations, the fort was built in the mid 1950s for the television show Tales of the 77th Bengal Lancers from Screen Gems, a Columbia Pictures subsidiary, erected at a cost of US$117,843.17. The set was torn down several years after the filming of "Arena", and the area is a parking lot across from the Vasquez Rocks Natural Area.

A piece of crinkled "stone" wall, which was black aluminum foil, was placed at the top of the frame to hide the California landscape with homes that would have otherwise been seen in one very wide shot of the fort. The remastered version of the episode corrects this error by rendering a CGI landscape in place of the foil.

Captain Kirk wears flat-soled, laced boots rather than the regular leather versions worn by the cast. Possibly the change was made for safety reasons given the many scenes in which Shatner scrambles over rocky ground.

Kirk also wears previously unseen white undergarments during the location segments on the asteroid. The long-sleeved shirt can be viewed just under the cuff of Kirk's tunic when he's using the recorder-translator. The "long johns" can be seen above the boots when Kirk is crouched on a rock. Given that this segment was filmed in November, the undergarments could be thermal, or perhaps padding for the fight scenes.

Cestus III was a globe of the Earth (previously seen in "Miri"), printed backwards and tinted a hazy orange.

The Enterprise's three double phaser bursts, which Sulu says constituted a full discharge of phaser banks, fire from an unusual location in this episode – not from near the glowing dome at the bottom of the saucer, but from much higher up, closer to where Matt Jefferies originally located the main phaser banks in his early diagrams of the ship. These schematics appeared as display diagrams in other episodes and also on the sides of the early AMTStar Trek model kits.

Phasers prove ineffective against the Gorn ship, so Kirk gives the order to arm the photon torpedoes, marking the first naming of that weapon in the series. Sulu says they get off a full discharging of photon torpedo "banks" in this episode, which constitutes only two shots, and they are red globular discharges that fire from the glowing dome under the saucer.

The closing credits use a different shot of Vina than was used for most of the first season episodes.

Both William Shatner and Leonard Nimoy currently suffer from tinnitus due to a special effects explosion on the set of this episode. DeForest Kelley reportedly suffered from tinnitus as well during the remainder of his life.

Filmation, who produced Star Trek: The Animated Series, went on to produce the hit cartoon He-Man and the Masters of the Universe (1983-85), which used many modified TAS character and set designs, a number of sound effects also utilized in both TOS and TAS, as well as having several Trek-similar story lines. The most notable of these is a second season episode called "The Arena", where a god-like entity forces He-Man and Skeletor to do battle, very similar to the Trek episode "Arena".

In the 1970s, the Mego toy company produced a "Gorn" action figure doll. However, unlike the TV character, the toy was dressed in the same costume used for the "Klingon" doll. Also, the head was the same one used for the Marvel Comics doll "The Lizard," except the Gorn head was molded brown to match the costume.

The creation of the diamond cannon was tested on the show MythBusters in late 2009 and deemed implausible. (It's been suggested the wood on the Metron planet may have had different properties, however).

"Arena" was the seventh episode of the remastered version of The Original Series to air. It premiered in syndication on the weekend of 21 October2006 and most notably featured new effects shots of Cestus III from space, the Enterprise battling the Gorn ship, and an expanded matte painting of the outpost, showing more battle damage and giving greater scope to the surrounding terrain. A small, but significant alteration also appeared in the form of the Gorn, which blinked several times throughout the remastered episode – achieved with computer-generated eyelids. Another small detail was finally inserted into the episode: the Gorn starship.